Summary of Work: Attention-deficit/hyperactivity disorder(ADHD)is perhaps the most common neurobehavioral disorder of childhood. The current estimate of prevalence is about 5% among elementary school children. Children with ADHD are hyperactive, impulsive and have difficulty keeping their attention focussed. These symptoms often limit their academic achievement and their ability to get along well with peers, teachers and parents. Many ADHD children, particularly those who go untreated, later develop severe behavioral, substance abuse, and mental health problems as adults. Few studies have looked at risk factors for ADHD in a population-based, rather than a highly selected clinic-based sample. The purpose of this project is to evaluate environmental, reproductive, and familial risk factors for ADHD within a population-based cohort. We plan to screen all the children in the Johnston County school system in grades 1-5 (N=7000). Johnston County is a semi-rural county Southeast of Raleigh. Our main hypotheses are that preterm delivery increases the risk of ADHD and that increased exposure to lead during childhood (measured either by matching with the N.C. blood lead testing registry or in exfoliated baby teeth) increases risk. We will also collect data on pregnancy complications and mother's exposures during pregnancy to alcohol, cigarette smoke and occupational exposures including solvents, metals, and pesticides. We will look for associations between well water contamination with nitrates and pesticides as well. Because ADHD is often poorly diagnosed, we plan to evaluate possible biases in the case identification process. Basic demographic information on the age, racial, and SES distribution of ADHD remains poorly described. We anticipate that this study will make an important contribution to the literature by describing reproductive,environmental, and familial risk factors in our sample.